Health officials are saying a tulsa dentist may have exposed thousands of patients to life-threatening diseases ranging from hiv to hepatitis. Abc's chief health and medical editor dr. Richard besser is here with this disturbing story. It is. I've spent my career in public health and it's not hard to presdrepts infections in dental offices but what they found here was absolutely shocking. Dr. W. Scott harrington has been a trusted oral surgeon for 36 years but now authorities believe he may have exposed thousands of patients to potentially deadly infection by allegedly using rusty instruments which weren't cleaned properly. Letters are being sent to 7,000 oklahoma patients recommending they immediately be tested for hepatitis b, hepatitis c and hiv. After one of his patients with no known risk factors tested positive for hepatitis c. In addition to allegations that he cleaned his instruments by improperly bleaching them which caused them to become porous over time he's also accused of reusing needles and vials. The instruments that came out of the autoclave were horrible. I wouldn't let my nephews play with them out in the dirt. They had rust on them. Reporter: He even reportedly had medications 20 years past their expiration date and allowed unlicensed assistants to give i.V. Medications. We reached out to the doctor but he did not return calls. 7,000 patients have gotten these letters to get tested for hiv, hepatitis c -- what is the indication more will test positive given those conditions? There are a couple of disturbing factors here. You know, many patients in his practice have hiv and hepatitis c -- he was treating a -- he was and had instruments set aside for those patients and other instruments for patients where he didn't know whether they were infected or not. That's very dangerous. All instruments should be treated the same. Last summer there were 8,000 patients from colorado who were notified and thankfully there none of them were infected. Here there's a much higher chance someone -- I would have thought soaking instruments in bleach would havekilled anything. We hear bleach is the only thing that -- for a lot bleach is the only way to go but these have to go into an autoclave. If you use bleach on them first it disturbs the outside of the instrument so the autoclave no longer works. And become porous. And heat and pressure don't kill the germs. What are you supposed to look for, rich? I go to a dentist office and usually I have so much stuff in my mouth I can't see what's going on. If you ever see rusty or old instruments, that's a warning sign. The other if dour dentist isn't wearing gloves or changing them between patients -- he should do that in front of me. Definitely. You should see that they're putting on fresh gloves, And pay attention to the instruments. Rich, thanks so much. Disturbing news. We'll keep on top of it.

This transcript has been automatically generated and may not be 100% accurate.

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